Ethylene pyrolysis involves the cracking of hydrocarbons and steam mixtures in a furnace to produce ethylene, a basic raw material used in the polymer and synthetic fiber industries. The process is usually carried out in tube coils heated to about 800.degree.-1000.degree. C.
Currently, cast alloy HK40 or wrought alloy 800 tubes are used. A recent trend in the industry is to improve throughput by increasing temperatures and decreasing the residence time. These demands call for an alloy having improved creep strength and carburization resistance to about 1100.degree. C.
It is also useful to employ internally finned tubes to increase the surface area of the piping. This technique further increases the efficiency of the pyrolysis process.
Current alloys tend to coke in certain cases. Decoking procedures require expensive down time.
There have been attempts to develop and/or adapt alloys for ethylene pyrolysis service. Alloys HK40, HPM and the 800 series have met with varying degrees of success.
The problem appears to be that the alloys carburize in service primary as a result of coking.
There is a need for an alloy especially adapted for ethylene pyrolysis operations.